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The ac on my 1989 tc Runs cold but periodically it seems like the vent closes - the fan keeps running but no air comes out -then after about a minutes the vents seem to open and all is normal again. This goes on and on like this. Any ideas?

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I'm guessing the air stops coming out of the front vents and starts coming out of the defroster vents which are the default.

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When you accelerate you loose vacuum and the air flow door closes and diverts the air to the defroster. This is as David said is by default.

There is a check valve in the vacuum lines that is supposed to minimize this. I replaced all of the vacuum lines and check valves in one of mine and it really made a big difference.

Good luck

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This is a common problem in older Volvos. I am not a mechanic but seem to recall the fix for them is to replace the brain (or system) that controls the flaps and that the piece had a number of air lines attached that ran to those flaps opening and closing them as needed when things worked right and not doing so when they did not.

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Ditto

When you accelerate you loose vacuum and the air flow door closes and diverts the air to the defroster. This is as David said is by default.

There is a check valve in the vacuum lines that is supposed to minimize this. I replaced all of the vacuum lines and check valves in one of mine and it really made a big difference.

Good luck

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Those answers sound realistic. Most likely the culprit is the vacuum selector switch in the heater control. There is no maintenance that can be done on the switch and the do no last forever.

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This is a common problem in older Volvos. I am not a mechanic but seem to recall the fix for them is to replace the brain (or system) that controls the flaps and that the piece had a number of air lines attached that ran to those flaps opening and closing them as needed when things worked right and not doing so when they did not.

Lucky thing there is no brain in a TC. (that could be possible even with a driver behind the wheel) ;)

There is a vacuum actuator, actually there are several but the one closest to the accelerator pedal, up under the dash on the HVAC unit is the one I'm referring to. It controls this operation and there is a good possibility that the diaphragm has developed a leak. They are replaceable, but difficult to do.

The check valve should be the first thing to check and likely replace.

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plym69 I had the same problem.Replaced the check valve.Now it works like it should.Replace the Check valve.

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Hi Robb 221 Which heater check valve and where is it located? Sorry, I'm new at this. Thanks Ken

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Hi plym69 sent you email.Let me know if you get it or if you have any problems.

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plym69,your loosing vacuum, check all lines from vacuum source and all connections, one way valve, function switch and air control door vacuum actuator.

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mine does this constantly and only when i need extra acceleration or "boost" from the engine. after about 10 seconds it settles down and air blows again on the upper vents... until i need extra engine oomph then is cycles this issue over and over.

 

rob221.... that picture looks like it is somewhere in the engine bay yet i cannot seem to find a check valve there like this. can you take a larger pic of this area so i can look in my engine bay for the valve?

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1 hour ago, gymowner said:

mine does this constantly and only when i need extra acceleration or "boost" from the engine. after about 10 seconds it settles down and air blows again on the upper vents... until i need extra engine oomph then is cycles this issue over and over.

 

If you read what I wrote May 16 2012 (above) and suspect this is the problem, PM me

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